This application claims priority of Europaen Patent Application No. 994600591, which was filed on Sep. 27, 1999.
1. Field of the Invention
This invention relates to a method for managing information transmission between a telecommunications terminal comprising a so-called xe2x80x9cblindxe2x80x9d radio and a base station of a telecommunications network, said method being used for switching bearers during this transmission. It is implemented in the field of wireless telecommunications network using a so-called xe2x80x9cblindxe2x80x9d radio.
2. Background of the Related Art
The invention will be described with reference to a DECT telecommunications network without this having to be considered as limiting the scope of the invention to this standard. In DECT systems, communications are transported over carrier frequencies, each having a frame structure. Three frequency bands are allocated to the DECT system. Each of these frequency bands is split into ten carrier frequencies. Each carrier is divided into 24 time intervals, twelve of which are used for transmission in the uplink direction (from terminal to base station) and the other twelve for transmission in the downlink direction (from base station to terminal). Conventionally, the link between a terminal and its base station is performed, in the downlink direction, on a first bearerxe2x80x94time interval n and carrier frequency cxe2x80x94and, in the uplink direction, on another bearer depending on the first onexe2x80x94time interval n+12 and carrier frequency cxe2x80x94.
Throughout the description, the pair composed of at least one time interval within the radio frame and a carrier frequency, whereon a radio link is established, will be called bearer. In the case of a telephone call (voice), bearers each comprise a single time interval. For data transportation, bearers can comprise several consecutive time intervals. Throughout the description, the bearer composed of time interval n and carrier frequency c is marked as [n;c] and the bearer composed of time intervals n and n+1 and carrier frequency c is marked as [(n,n+1);c].
When interference comes up disrupting the radio link between the terminal and the base station, it is sometimes required to switch bearers. The terminal then starts to search for a new bearer whereon the radio link will not be disrupted. When a new bearer has been found, the communication between the terminal and the base station is transferred onto this new bearer by reprogramming the radio of the terminal and the base station on this new bearer.
During the search for a new bearer, the terminal radio must process simultaneously the bearer signals of the disrupted link and those of the new potential bearer. Due to this dual processing, it appears that using a so-called xe2x80x9cblindxe2x80x9d radio in the terminals significantly limits the number of new potential bearers. Indeed, so-called xe2x80x9cblindxe2x80x9d radios specify the radios that cannot process the signals contained in two consecutive time intervals. As a result, such a radio, also called blind radio, cannot search for a new bearer comprising a time interval adjacent to that of the bearer already used. This impossibility is illustrated on a DECT frame represented in FIG. 1. In this carrier frequency c DECT frame, the bearers [6;c] and [18;c] are allocated to transmitting information between the terminal and the base station, respectively in the downlink and uplink directions. If, for any reason, bearer [6;c] (or bearer [18;c]) must be switched, the terminal""s xe2x80x9cblindxe2x80x9d radio is not capable of processing simultaneously bearer [6;c] and bearer [5;c] or [7;c] (respectively [17;c] or [19;c]). Neither will it be able to process bearer [5;cxe2x80x2], [6;cxe2x80x2] or [7;cxe2x80x2] (respectively [ 17;cxe2x80x2], [ 18;cxe2x80x2] or [ 19;cxe2x80x2]) with cxe2x80x2 designating a carrier frequency different from c. Therefore, the terminal must search for a new bearer among the other bearers available. The new bearers [5;c] and [7;c] (respectively [17;c] and [19;c] prohibited by the xe2x80x9cblindxe2x80x9d radio are rasterized in the DECT frame of FIG. 1.
Consequently, a xe2x80x9cblindxe2x80x9d radio significantly limits the bearer switching capacities. This may result in blocking situations when the remaining bearers are already being used for other calls.
It should be noted, in FIG. 1, that exchanges between the terminal and the base station are performed in each direction for a single time interval. This data exchange protocol is commonly called LU1. In particular, it is used for transporting voice (telephone call). FIG. 2 illustrates a second data exchange protocol commonly called LU7, wherein exchanges are performed in each direction for two consecutive time intervals. This bearer then comprises two adjacent time intervals and a carrier frequency. For clarity""s sake, this is then called a dual bearer to distinguish them from single bearers comprising a single time interval. FIG. 2 represents a DECT frame of carrier frequency c. A terminal and a base station communicate over the dual bearer [(6,7);c] in the downlink direction and the dual bearer [(18,19);c] in the uplink direction. According to this protocol, the number of the first of two consecutive time intervals must be even. In this example, if the terminal is supposed to be fitted with a xe2x80x9cblindxe2x80x9d radio, the new dual bearers comprising the single bearers [5;c or cxe2x80x2] and [8;c or cxe2x80x2] are prohibited. In addition, as the number of the first time interval of the new dual bearer must be even, the choice of new dual bearers is even more restricted.
If it is presumed that no other terminal is communicating, there are 3xc3x9710 new potential dual bearers left:
[(0,1);c],
[(2,3);c] where c is any carrier frequency
[(10,11);c]
Blocking situations can occur when other terminals are communicating. A blocking example on a carrier frequency c is illustrated by FIG. 3. The dual bearer [(6,7);c] is used for transporting data and the single bearers [0;c], [3;c] and [11;c] (hatched in the frame of FIG. 3) are used for transporting telephone calls. If for any reason, it is required to switch dual bearers, there is no other possibility on this carrier because of the constraints imposed by the blind radio and the LU7 protocol.
It is the object of the invention to provide a transmission management method allowing to reduce the number of blocking situations during bearer switching.
It is another object to provide a method allowing to increase traffic in the telecommunications network comprising terminals fitted with xe2x80x9cblindxe2x80x9d radios.
Moreover, according to the invention, it is proposed to disconnect the xe2x80x9cblindxe2x80x9d radio of the terminal when searching for a new bearer so as to avoid the possibility of establishing a link on a new bearer with a time interval adjacent to that of the bearer already being used.
For this purpose, the object of the invention is a method for managing information transmission via successive radio frames between a telecommunications terminal comprising a so-called xe2x80x9cblindxe2x80x9d radio and a base station of a telecommunications network, each radio frame comprising a plurality of bearers, each defined by at least one time interval within the radio frame and a carrier frequency, said information transmission being performed on the first bearer, said method being used for bearer switching during said transmission and comprising a step of searching for a new bearer available and a step of programming the so-called xe2x80x9cblindxe2x80x9d radio on said new bearer, characterized in that said search step is taking place on a limited number of radio frames, and in that, during this step, the programming of the so-called xe2x80x9cblindxe2x80x9d radio on said first bearer is interrupted.
In this way, the new bearers can be defined for time intervals adjacent to that (or those, in case of a first dual bearer) of the first bearer.
According to a preferred embodiment, the information contained in the radio frames not received by the terminal during the search step are saved in a buffer memory of the base station during this step, then retransmitted to the terminal after the link has been established on the new bearer.